﻿#if NET40
// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// TransformBlock.cs
//
//
// A propagator block that runs a function on each input to produce a single output.
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Diagnostics.Contracts;
using System.Threading.Tasks.Dataflow.Internal;

namespace System.Threading.Tasks.Dataflow
{
  /// <summary>Provides a dataflow block that invokes a provided <see cref="System.Func{TInput,TOutput}"/> delegate for every data element received.</summary>
  /// <typeparam name="TInput">Specifies the type of data received and operated on by this <see cref="TransformBlock{TInput,TOutput}"/>.</typeparam>
  /// <typeparam name="TOutput">Specifies the type of data output by this <see cref="TransformBlock{TInput,TOutput}"/>.</typeparam>
  [DebuggerDisplay("{DebuggerDisplayContent,nq}")]
  [DebuggerTypeProxy(typeof(TransformBlock<,>.DebugView))]
  public sealed class TransformBlock<TInput, TOutput> : IPropagatorBlock<TInput, TOutput>, IReceivableSourceBlock<TOutput>, IDebuggerDisplay
  {
    #region @@ Fields @@

    /// <summary>The target side.</summary>
    private readonly TargetCore<TInput> _target;

    /// <summary>Buffer used to reorder outputs that may have completed out-of-order between the target half and the source half.</summary>
    private readonly ReorderingBuffer<TOutput> _reorderingBuffer;

    /// <summary>The source side.</summary>
    private readonly SourceCore<TOutput> _source;

    /// <summary>Gets the object to use for writing to the source when multiple threads may be involved.</summary>
    /// <remarks>
    /// If a reordering buffer is used, it is safe for multiple threads to write to concurrently and handles safe 
    /// access to the source. If there's no reordering buffer because no parallelism is used, then only one thread at
    /// a time will try to access the source, anyway.  But, if there's no reordering buffer and parallelism is being
    /// employed, then multiple threads may try to access the source concurrently, in which case we need to manually
    /// synchronize all such access, and this lock is used for that purpose.
    /// </remarks>
    private object ParallelSourceLock { get { return _source; } }

    #endregion

    #region @@ Properties @@

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Targets/Member[@name="InputCount"]/*' />
    public Int32 InputCount { get { return _target.InputCount; } }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="OutputCount"]/*' />
    public Int32 OutputCount { get { return _source.OutputCount; } }

    #endregion

    #region @@ Constructors @@

    /// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>.</summary>
    /// <param name="transform">The function to invoke with each data element received.</param>
    /// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
    public TransformBlock(Func<TInput, TOutput> transform) :
      this(transform, null, ExecutionDataflowBlockOptions.Default)
    { }

    /// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/> 
    /// and <see cref="ExecutionDataflowBlockOptions"/>.</summary>
    /// <param name="transform">The function to invoke with each data element received.</param>
    /// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
    /// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
    /// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
    public TransformBlock(Func<TInput, TOutput> transform, ExecutionDataflowBlockOptions dataflowBlockOptions) :
      this(transform, null, dataflowBlockOptions)
    { }

    /// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>.</summary>
    /// <param name="transform">The function to invoke with each data element received.</param>
    /// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
    [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")]
    public TransformBlock(Func<TInput, Task<TOutput>> transform) :
      this(null, transform, ExecutionDataflowBlockOptions.Default)
    { }

    /// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>
    /// and <see cref="ExecutionDataflowBlockOptions"/>.</summary>
    /// <param name="transform">The function to invoke with each data element received.</param>
    /// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
    /// <exception cref="System.ArgumentNullException">The <paramref name="transform"/> is null (Nothing in Visual Basic).</exception>
    /// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
    [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")]
    public TransformBlock(Func<TInput, Task<TOutput>> transform, ExecutionDataflowBlockOptions dataflowBlockOptions) :
      this(null, transform, dataflowBlockOptions)
    { }

    #endregion

    #region ** TransformBlock **

    /// <summary>Initializes the <see cref="TransformBlock{TInput,TOutput}"/> with the specified <see cref="System.Func{TInput,TOutput}"/>
    /// and <see cref="DataflowBlockOptions"/>.</summary>
    /// <param name="transformSync">The synchronous function to invoke with each data element received.</param>
    /// <param name="transformAsync">The asynchronous function to invoke with each data element received.</param>
    /// <param name="dataflowBlockOptions">The options with which to configure this <see cref="TransformBlock{TInput,TOutput}"/>.</param>
    /// <exception cref="System.ArgumentNullException">The <paramref name="transformSync"/> and <paramref name="transformAsync"/> are both null (Nothing in Visual Basic).</exception>
    /// <exception cref="System.ArgumentNullException">The <paramref name="dataflowBlockOptions"/> is null (Nothing in Visual Basic).</exception>
    private TransformBlock(Func<TInput, TOutput> transformSync, Func<TInput, Task<TOutput>> transformAsync, ExecutionDataflowBlockOptions dataflowBlockOptions)
    {
      if (transformSync == null && transformAsync == null) { throw new ArgumentNullException("transform"); }
      if (dataflowBlockOptions == null) { throw new ArgumentNullException(nameof(dataflowBlockOptions)); }

      Debug.Assert(transformSync == null ^ transformAsync == null, "Exactly one of transformSync and transformAsync must be null.");
      Contract.EndContractBlock();

      // Ensure we have options that can't be changed by the caller
      dataflowBlockOptions = dataflowBlockOptions.DefaultOrClone();

      // Initialize onItemsRemoved delegate if necessary
      Action<ISourceBlock<TOutput>, Int32> onItemsRemoved = null;
      if (dataflowBlockOptions.BoundedCapacity > 0)
      {
        onItemsRemoved = (owningSource, count) => ((TransformBlock<TInput, TOutput>)owningSource)._target.ChangeBoundingCount(-count);
      }

      // Initialize source component.
      _source = new SourceCore<TOutput>(this, dataflowBlockOptions,
          owningSource => ((TransformBlock<TInput, TOutput>)owningSource)._target.Complete(exception: null, dropPendingMessages: true),
          onItemsRemoved);

      // If parallelism is employed, we will need to support reordering messages that complete out-of-order.
      // However, a developer can override this with EnsureOrdered == false.
      if (dataflowBlockOptions.SupportsParallelExecution && dataflowBlockOptions.EnsureOrdered)
      {
        _reorderingBuffer = new ReorderingBuffer<TOutput>(this, (owningSource, message) => ((TransformBlock<TInput, TOutput>)owningSource)._source.AddMessage(message));
      }

      // Create the underlying target
      if (transformSync != null) // sync
      {
        _target = new TargetCore<TInput>(this,
            messageWithId => ProcessMessage(transformSync, messageWithId),
            _reorderingBuffer, dataflowBlockOptions, TargetCoreOptions.None);
      }
      else // async
      {
        Debug.Assert(transformAsync != null, "Incorrect delegate type.");
        _target = new TargetCore<TInput>(this,
            messageWithId => ProcessMessageWithTask(transformAsync, messageWithId),
            _reorderingBuffer, dataflowBlockOptions, TargetCoreOptions.UsesAsyncCompletion);
      }

      // Link up the target half with the source half.  In doing so,
      // ensure exceptions are propagated, and let the source know no more messages will arrive.
      // As the target has completed, and as the target synchronously pushes work
      // through the reordering buffer when async processing completes,
      // we know for certain that no more messages will need to be sent to the source.
#if !NET40
      _target.Completion.ContinueWith((completed, state) =>
      {
        var sourceCore = (SourceCore<TOutput>)state;
        if (completed.IsFaulted) { sourceCore.AddAndUnwrapAggregateException(completed.Exception); }
        sourceCore.Complete();
      }, _source, CancellationToken.None, Common.GetContinuationOptions(), TaskScheduler.Default);
#else
      Action<Task> continuationAction1 = completed =>
      {
        if (completed.IsFaulted) { _source.AddAndUnwrapAggregateException(completed.Exception); }
        _source.Complete();
      };
      _target.Completion.ContinueWith(continuationAction1, CancellationToken.None, Common.GetContinuationOptions(), TaskScheduler.Default);
#endif

      // It is possible that the source half may fault on its own, e.g. due to a task scheduler exception.
      // In those cases we need to fault the target half to drop its buffered messages and to release its
      // reservations. This should not create an infinite loop, because all our implementations are designed
      // to handle multiple completion requests and to carry over only one.
#if !NET40
      _source.Completion.ContinueWith((completed, state) =>
      {
        var thisBlock = ((TransformBlock<TInput, TOutput>)state) as IDataflowBlock;
        Debug.Assert(completed.IsFaulted, "The source must be faulted in order to trigger a target completion.");
        thisBlock.Fault(completed.Exception);
      }, this, CancellationToken.None, Common.GetContinuationOptions() | TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default);
#else
      Action<Task> continuationAction2 = completed =>
      {
        var thisBlock = this as IDataflowBlock;
        Debug.Assert(completed.IsFaulted, "The source must be faulted in order to trigger a target completion.");
        thisBlock.Fault(completed.Exception);
      };
      _source.Completion.ContinueWith(continuationAction2, CancellationToken.None, Common.GetContinuationOptions() | TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default);
#endif
      // Handle async cancellation requests by declining on the target
      Common.WireCancellationToComplete(
          dataflowBlockOptions.CancellationToken, Completion, state => ((TargetCore<TInput>)state).Complete(exception: null, dropPendingMessages: true), _target);
#if FEATURE_TRACING
      var etwLog = DataflowEtwProvider.Log;
      if (etwLog.IsEnabled())
      {
        etwLog.DataflowBlockCreated(this, dataflowBlockOptions);
      }
#endif
    }

    #endregion

    #region ** ProcessMessage **

    /// <summary>Processes the message with a user-provided transform function that returns a TOutput.</summary>
    /// <param name="transform">The transform function to use to process the message.</param>
    /// <param name="messageWithId">The message to be processed.</param>
    private void ProcessMessage(Func<TInput, TOutput> transform, KeyValuePair<TInput, Int64> messageWithId)
    {
      // Process the input message to get the output message
      var outputItem = default(TOutput);
      var itemIsValid = false;
      try
      {
        outputItem = transform(messageWithId.Key);
        itemIsValid = true;
      }
      catch (Exception exc)
      {
        // If this exception represents cancellation, swallow it rather than shutting down the block.
        if (!Common.IsCooperativeCancellation(exc)) { throw; }
      }
      finally
      {
        // If we were not successful in producing an item, update the bounding
        // count to reflect that we're done with this input item.
        if (!itemIsValid) { _target.ChangeBoundingCount(-1); }

        // If there's no reordering buffer (because we're running sequentially or ordering was disabled),
        // simply pass the output message through. Otherwise, there's a reordering buffer, 
        // so add to it instead (if a reordering buffer is used, we always need
        // to output the message to it, even if the operation failed and outputMessage
        // is null... this is because the reordering buffer cares about a strict sequence
        // of IDs, and it needs to know when a particular ID has completed. It will eliminate
        // null messages accordingly.)
        if (_reorderingBuffer == null)
        {
          if (itemIsValid)
          {
            if (_target.DataflowBlockOptions.MaxDegreeOfParallelism == 1)
            {
              _source.AddMessage(outputItem);
            }
            else
            {
              lock (ParallelSourceLock)
              {
                _source.AddMessage(outputItem);
              }
            }
          }
        }
        else
        {
          _reorderingBuffer.AddItem(messageWithId.Value, outputItem, itemIsValid);
        }
      }
    }

    #endregion

    #region ** ProcessMessageWithTask **

    /// <summary>Processes the message with a user-provided transform function that returns a task of TOutput.</summary>
    /// <param name="transform">The transform function to use to process the message.</param>
    /// <param name="messageWithId">The message to be processed.</param>
    [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
    private void ProcessMessageWithTask(Func<TInput, Task<TOutput>> transform, KeyValuePair<TInput, Int64> messageWithId)
    {
      Debug.Assert(transform != null, "Function to invoke is required.");

      // Run the transform function to get the task that represents the operation's completion
      Task<TOutput> task = null;
      Exception caughtException = null;
      try
      {
        task = transform(messageWithId.Key);
      }
      catch (Exception exc) { caughtException = exc; }

      // If no task is available, we're done.
      if (task == null)
      {
        // If we didn't get a task because an exception occurred,
        // store it (if the exception was cancellation, just ignore it).
        if (caughtException != null && !Common.IsCooperativeCancellation(caughtException))
        {
          Common.StoreDataflowMessageValueIntoExceptionData(caughtException, messageWithId.Key);
          _target.Complete(caughtException, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: false);
        }

        // If there's a reordering buffer, notify it that this message is done.
        if (_reorderingBuffer != null) { _reorderingBuffer.IgnoreItem(messageWithId.Value); }

        // Signal that we're done this async operation, and remove the bounding
        // count for the input item that didn't yield any output.
        _target.SignalOneAsyncMessageCompleted(boundingCountChange: -1);
        return;
      }

      // Otherwise, join with the asynchronous operation when it completes.
#if !NET40
      task.ContinueWith((completed, state) =>
      {
        var tuple = (Tuple<TransformBlock<TInput, TOutput>, KeyValuePair<TInput, Int64>>)state;
        tuple.Item1.AsyncCompleteProcessMessageWithTask(completed, tuple.Item2);
      }, Tuple.Create(this, messageWithId), CancellationToken.None,
      Common.GetContinuationOptions(TaskContinuationOptions.ExecuteSynchronously), TaskScheduler.Default);
#else
      Action<Task<TOutput>> continuationAction = completed =>
      {
        AsyncCompleteProcessMessageWithTask(completed, messageWithId);
      };
      task.ContinueWith(continuationAction, CancellationToken.None,
        Common.GetContinuationOptions(TaskContinuationOptions.ExecuteSynchronously), TaskScheduler.Default);
#endif
    }

    #endregion

    #region ** AsyncCompleteProcessMessageWithTask **

    /// <summary>Completes the processing of an asynchronous message.</summary>
    /// <param name="completed">The completed task storing the output data generated for an input message.</param>
    /// <param name="messageWithId">The originating message</param>
    private void AsyncCompleteProcessMessageWithTask(Task<TOutput> completed, KeyValuePair<TInput, Int64> messageWithId)
    {
      Debug.Assert(completed != null, "Completed task is required.");
      Debug.Assert(completed.IsCompleted, "Task must be completed to be here.");

      var isBounded = _target.IsBounded;
      var gotOutputItem = false;
      var outputItem = default(TOutput);

      switch (completed.Status)
      {
        case TaskStatus.RanToCompletion:
          outputItem = completed.Result;
          gotOutputItem = true;
          break;

        case TaskStatus.Faulted:
          // We must add the exception before declining and signaling completion, as the exception
          // is part of the operation, and the completion conditions depend on this.
          var aggregate = completed.Exception;
          Common.StoreDataflowMessageValueIntoExceptionData(aggregate, messageWithId.Key, targetInnerExceptions: true);
          _target.Complete(aggregate, dropPendingMessages: true, storeExceptionEvenIfAlreadyCompleting: true, unwrapInnerExceptions: true);
          break;
          // Nothing special to do for cancellation
      }

      // Adjust the bounding count if necessary (we only need to decrement it for faulting
      // and cancellation, since in the case of success we still have an item that's now in the output buffer).
      // Even though this is more costly (again, only in the non-success case, we do this before we store the
      // message, so that if there's a race to remove the element from the source buffer, the count is
      // appropriately incremented before it's decremented.
      if (!gotOutputItem && isBounded) { _target.ChangeBoundingCount(-1); }

      // If there's no reordering buffer (because we're running sequentially or ordering is disabled),
      // and we got a message, simply pass the output message through.
      if (_reorderingBuffer == null)
      {
        if (gotOutputItem)
        {
          if (_target.DataflowBlockOptions.MaxDegreeOfParallelism == 1)
          {
            _source.AddMessage(outputItem);
          }
          else
          {
            lock (ParallelSourceLock)
            {
              _source.AddMessage(outputItem);
            }
          }
        }
      }
      // Otherwise, there's a reordering buffer, so add to it instead.
      // Even if something goes wrong, we need to update the
      // reordering buffer, so it knows that an item isn't missing.
      else
      {
        _reorderingBuffer.AddItem(messageWithId.Value, outputItem, itemIsValid: gotOutputItem);
      }

      // Let the target know that one of the asynchronous operations it launched has completed.
      _target.SignalOneAsyncMessageCompleted();
    }

    #endregion

    #region -- IDataflowBlock Members --

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Completion"]/*' />
    public Task Completion { get { return _source.Completion; } }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Complete"]/*' />
    public void Complete()
    {
      _target.Complete(exception: null, dropPendingMessages: false);
    }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="Fault"]/*' />
    void IDataflowBlock.Fault(Exception exception)
    {
      if (exception == null) throw new ArgumentNullException(nameof(exception));
      Contract.EndContractBlock();

      _target.Complete(exception, dropPendingMessages: true);
    }

    #endregion

    #region -- IReceivableSourceBlock Members --

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="TryReceive"]/*' />
    public Boolean TryReceive(Predicate<TOutput> filter, out TOutput item)
    {
      return _source.TryReceive(filter, out item);
    }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="TryReceiveAll"]/*' />
    public Boolean TryReceiveAll(out IList<TOutput> items)
    {
      return _source.TryReceiveAll(out items);
    }

    #endregion

    #region -- ITargetBlock Members --

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Targets/Member[@name="OfferMessage"]/*' />
    DataflowMessageStatus ITargetBlock<TInput>.OfferMessage(DataflowMessageHeader messageHeader, TInput messageValue, ISourceBlock<TInput> source, Boolean consumeToAccept)
    {
      return _target.OfferMessage(messageHeader, messageValue, source, consumeToAccept);
    }

    #endregion

    #region -- ISourceBlock Members --

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="LinkTo"]/*' />
    public IDisposable LinkTo(ITargetBlock<TOutput> target, DataflowLinkOptions linkOptions)
    {
      return _source.LinkTo(target, linkOptions);
    }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ConsumeMessage"]/*' />
    TOutput ISourceBlock<TOutput>.ConsumeMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target, out Boolean messageConsumed)
    {
      return _source.ConsumeMessage(messageHeader, target, out messageConsumed);
    }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ReserveMessage"]/*' />
    Boolean ISourceBlock<TOutput>.ReserveMessage(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target)
    {
      return _source.ReserveMessage(messageHeader, target);
    }

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Sources/Member[@name="ReleaseReservation"]/*' />
    void ISourceBlock<TOutput>.ReleaseReservation(DataflowMessageHeader messageHeader, ITargetBlock<TOutput> target)
    {
      _source.ReleaseReservation(messageHeader, target);
    }

    #endregion

    #region -- ToString --

    /// <include file='XmlDocs/CommonXmlDocComments.xml' path='CommonXmlDocComments/Blocks/Member[@name="ToString"]/*' />
    public override String ToString()
    {
      return Common.GetNameForDebugger(this, _source.DataflowBlockOptions);
    }

    #endregion

    #region -- IDebuggerDisplay Members --

    /// <summary>Gets the number of messages waiting to be processed.  This must only be used from the debugger as it avoids taking necessary locks.</summary>
    private Int32 InputCountForDebugger { get { return _target.GetDebuggingInformation().InputCount; } }

    /// <summary>Gets the number of messages waiting to be processed.  This must only be used from the debugger as it avoids taking necessary locks.</summary>
    private Int32 OutputCountForDebugger { get { return _source.GetDebuggingInformation().OutputCount; } }

    /// <summary>The data to display in the debugger display attribute.</summary>
    [SuppressMessage("Microsoft.Globalization", "CA1305:SpecifyIFormatProvider")]
    private Object DebuggerDisplayContent
    {
      get
      {
        return "{0}, InputCount={1}, OutputCount={2}".FormatWith(
            Common.GetNameForDebugger(this, _source.DataflowBlockOptions),
            InputCountForDebugger,
            OutputCountForDebugger);
      }
    }

    /// <summary>Gets the data to display in the debugger display attribute for this instance.</summary>
    Object IDebuggerDisplay.Content { get { return DebuggerDisplayContent; } }

    #endregion

    #region ** class DebugView **

    /// <summary>Provides a debugger type proxy for the TransformBlock.</summary>
    private sealed class DebugView
    {
      /// <summary>The transform being viewed.</summary>
      private readonly TransformBlock<TInput, TOutput> _transformBlock;

      /// <summary>The target half of the block being viewed.</summary>
      private readonly TargetCore<TInput>.DebuggingInformation _targetDebuggingInformation;

      /// <summary>The source half of the block being viewed.</summary>
      private readonly SourceCore<TOutput>.DebuggingInformation _sourceDebuggingInformation;

      /// <summary>Initializes the debug view.</summary>
      /// <param name="transformBlock">The transform being viewed.</param>
      public DebugView(TransformBlock<TInput, TOutput> transformBlock)
      {
        Debug.Assert(transformBlock != null, "Need a block with which to construct the debug view.");
        _transformBlock = transformBlock;
        _targetDebuggingInformation = transformBlock._target.GetDebuggingInformation();
        _sourceDebuggingInformation = transformBlock._source.GetDebuggingInformation();
      }

      /// <summary>Gets the messages waiting to be processed.</summary>
      public IEnumerable<TInput> InputQueue { get { return _targetDebuggingInformation.InputQueue; } }

      /// <summary>Gets any postponed messages.</summary>
      public QueuedMap<ISourceBlock<TInput>, DataflowMessageHeader> PostponedMessages { get { return _targetDebuggingInformation.PostponedMessages; } }

      /// <summary>Gets the messages waiting to be received.</summary>
      public IEnumerable<TOutput> OutputQueue { get { return _sourceDebuggingInformation.OutputQueue; } }

      /// <summary>Gets the number of outstanding input operations.</summary>
      public Int32 CurrentDegreeOfParallelism { get { return _targetDebuggingInformation.CurrentDegreeOfParallelism; } }

      /// <summary>Gets the task being used for output processing.</summary>
      public Task TaskForOutputProcessing { get { return _sourceDebuggingInformation.TaskForOutputProcessing; } }

      /// <summary>Gets the DataflowBlockOptions used to configure this block.</summary>
      public ExecutionDataflowBlockOptions DataflowBlockOptions { get { return _targetDebuggingInformation.DataflowBlockOptions; } }

      /// <summary>Gets whether the block is declining further messages.</summary>
      public Boolean IsDecliningPermanently { get { return _targetDebuggingInformation.IsDecliningPermanently; } }

      /// <summary>Gets whether the block is completed.</summary>
      public Boolean IsCompleted { get { return _sourceDebuggingInformation.IsCompleted; } }

      /// <summary>Gets the block's Id.</summary>
      public Int32 Id { get { return Common.GetBlockId(_transformBlock); } }

      /// <summary>Gets the set of all targets linked from this block.</summary>
      public TargetRegistry<TOutput> LinkedTargets { get { return _sourceDebuggingInformation.LinkedTargets; } }

      /// <summary>Gets the target that holds a reservation on the next message, if any.</summary>
      public ITargetBlock<TOutput> NextMessageReservedFor { get { return _sourceDebuggingInformation.NextMessageReservedFor; } }
    }

    #endregion
  }
}
#endif